10 On the Modifications of Clouds , &c. 



this idea: yet it is in a great measure confirmed by ob-» 

 servations made in various ways upon the electrical state of 

 clouds and of rain, not to insist on the probability that a 

 thunder storm is only a more sudden and sensible display 

 of those energies which, according to the order observable 

 in the creation in other respects, ought to be incessantly 

 and silently operating for more general and beneficial pur- 

 poses. 



In the formation of the nimbus, two circumstances claim 

 particular attention : the spreading of the superior masses 

 of cloud in all directions until they become, like the stratus, 

 one uniform sheet ; and the rapid motion and visible de- 

 crease of the cumulus when brought under the latter. The 

 cirri, also, which so frequently stretch from the superior 

 sheet upward, and resemble erected hairs, carry so much 

 the appearance of temporarv conductors for the electricity, 

 extricated by the sudden union of its minute drops into the 

 vastly larger ones which form the rain, that one is in a 

 manner compelled, when viewing this phaenomenon, to in- 

 dulge a little in electrical speculations. By one experiment 

 of Cavallo's, with a kite carrying three hundred and sixty 

 feet of conducting string, in an interval between two 

 showers, and kept up durina; rain, it seems that the su- 

 perior clouds possessed a positive electricity before the rain, 

 which on the arrival of a large cumulus gave place to a very 

 strong negative, continuing as long as it was over the kite. 

 We are not, however, warranted from this to conclude the 

 cumulus which brings on rain always negative, as the same 

 effect might ensue from a positive cumulus uniting with a 

 negative stratus. Yet the general negative state of the lower 

 atmosphere during rain, and ^^t positive indications com- 

 monly given bv the true stratus, render this the more pro- 

 bable opinion. It is not, however, absolutelv necessary to 

 determine the several states of the clouds which appear 

 dur.ng rain, since there is sufficient evidence in favour of 

 the conclusion, that clouds formed in dii^ercut parts of the 

 atmosphere operate on each other, when brought near 

 enough, so as lo occasion their pariial or entire destruction ; 

 an etiect which can only be attributed to their possessing 

 beforehand, or acquiring at the moment, the opposite elec- 

 tricities. 



It may be objected that this explanation is better suited 

 to the case of a shower than to that of continued mln, for 

 which it docs not seem sufticient. If it should appear,, 

 nevcrlhclcss, that the supply of each kiiid of cloud is by 

 any means kept up in proportion to the consumption, the 

 5 objection 



